M1.6 tap drill size
The tap drill for M1.6×0.35 is 1.25 mm. That’s the standard chart size and gives about 77% of full thread.
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Tap drill by thread percentage
75% is the usual workshop figure. Less thread is easier to tap; more adds little strength.
| Thread % | Ideal drill | Nearest metric drill | Nearest imperial drill |
|---|---|---|---|
| 60% | 1.327 mm 0.0523" | 1.35 mm (55%) | #55 0.0520" (61%) |
| 65% | 1.304 mm 0.0514" | 1.3 mm (66%) | #55 0.0520" (61%) |
| 70% | 1.282 mm 0.0505" | 1.3 mm (66%) | #55 0.0520" (61%) |
| 75% | 1.259 mm 0.0496" | 1.25 mm (77%) | #55 0.0520" (61%) |
| 80% | 1.236 mm 0.0487" | 1.25 mm (77%) | 3/64" 0.0469" (90%) |
About this size
ISO metric coarse is the default thread for general engineering in the UK and Europe. If a drawing just says “M10”, it means the coarse pitch.
- Taps this small snap easily. By hand, or in stainless steel, a 1.3 mm drill (about 66% thread) makes tapping much easier for very little loss of strength.
- For a blind hole with 1.5 × D thread engagement (2.4 mm), drill about 3.8 mm deep. That leaves room for the 3–4 tapered lead threads on a second or plug tap. In steel, 1 × D engagement is usually enough; in aluminium or cast iron allow 1.5–2 × D.
Clearance holes for M1.6
| Fit | Drill |
|---|---|
| Close | 1.7 mm (0.067") |
| Medium (normal) | 1.8 mm (0.071") |
| Free (loose) | 2 mm (0.079") |
Fine, medium and coarse series from ISO 273. Medium suits most jobs; use fine where parts must locate closely and coarse for quick assembly or coated bolts.
M1.6 thread data
| Designation | M1.6×0.35 |
|---|---|
| Standard | ISO 68-1 basic profile, ISO 261/262 series |
| Pitch | 0.35 mm pitch (72.6 TPI equivalent) |
| Thread angle | 60° |
| Major diameter | 1.6 mm (0.063") |
| Pitch (effective) diameter | 1.373 mm (0.054") |
| Minor diameter, external | 1.171 mm (0.046") |
| Minor diameter, internal | 1.221 mm (0.048") |
| Thread depth (internal) | 0.189 mm |
Basic sizes. Real screws are slightly under and real nuts slightly over these values because of tolerance classes.
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Nearest alternatives
If you don’t have the right drill, these give:
- 1.2 mm drill → about 88% thread
- 1.25 mm drill → about 77% thread
- 1.3 mm drill → about 66% thread
Threads close in size (not interchangeable – the pitch and/or angle differ):
- 10BA – 1.7 mm major, 0.35 mm pitch (72.6 TPI equivalent)
Questions
What size drill for a M1.6 tap?
The tap drill for M1.6×0.35 is 1.25 mm. That’s the standard chart size and gives about 77% of full thread.
What size clearance hole for M1.6?
For a M1.6 screw or bolt, drill 1.7 mm for a close fit, 1.8 mm for a medium (normal) fit or 2 mm for a free fit. These are the ISO 273 fine, medium and coarse sizes.
What is the pitch of M1.6?
M1.6×0.35 has a 0.35 mm pitch (72.6 TPI equivalent), a 60° thread angle and a 1.6 mm major diameter.
Sources: Chart drill: the common metric coarse tapping chart. Percent values worked out from the ISO 68-1 basic profile. Clearance holes: ISO 273 (checked 25/10/2026). Values are for reference only – check your tap maker’s chart. See the disclaimer.
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